This chapter covers theories of the modern information age in a number of steps: First, there is a description of some of the intellectual precursors that give rise to the notion that we are living in an information or knowledge age. Second, an enumeration of some of the perspectives that lead to the idea of modern societies as knowledge or information societies. Third, the usage of the term knowledge, defined as a capacity for action is explicated in greater detail. Fourth, the core sections of the article deal with the theory of the knowledge and the information society as well as some of its competitors such as the network society. The article presents the argument that advanced societies are best conceptualized as knowledge societies, last but not least because economic growth, social change and inequality generally but also the nature of social conflicts and identity formation are increasingly generated by knowledge. That is, knowledge does not merely open up the secrets of nature and society but is the becoming of a world.